Objectives. Physical activity declines during adolescence. The Theory of Planned Behaviour is a useful framework for investigating activity, but leaves variance unexplained. We explored the utility of a dual-process approach by using the Theory of Planned Behaviour and the Prototype Willingness Model to investigate correlates of physical activity, and of one-year change in physical activity, among a large sample of adolescents. Design. A cross-sectional and longitudinal analysis of baseline and follow-up data from the Fit to Study cluster-randomised trial. Methods. 9,699 secondary school pupils at baseline and 4,632 at follow-up (mean age=12.5 years) completed measures of past week physical activity and constructs from the two behaviour-change models, at time-points one year apart. Cross-sectional analyses used multilevel, stepwise models to measure strength of associations between model constructs and physical activity, and variance in behaviour explained by Prototype Willingness Model over and above Theory of Planned Behaviour. In longitudinal analyses, change scores were calculated by subtracting follow-up from baseline scores. Models controlling for trial treatment status measured strength of associations between change scores, and variance explained. Results. At baseline, after controlling for past behaviour, physically-active prototype similarity had the strongest relationship with activity after intention to be active. Change in prototype similarity had the strongest relationship with change in activity after change in intention and attitudes. Prototype perceptions and willingness explained additional variance in behaviour. Conclusion. A dual-process model incorporating prototype perceptions could more usefully predict physical activity than models based on rational expectations alone. Behaviour-change interventions promoting an active self-image could be tested for effects on physical activity. Key words: Theory of Planned Behaviour, Prototype Willingness Model, physical activity, adolescent, behaviour-change.
Wheatley, Catherine M.Wassenaar, ThomasBeale, Nick Salvan, PiergiorgioDawes, HelenDavies, Emma Johansen-Berg, Heidi
Department of Sport, Health Sciences and Social WorkDepartment of Psychology, Health and Professional Development
Year of publication: 2022Date of RADAR deposit: 2022-01-17